The present invention relates generally to controllers for industrial processes and in particular to a human-machine interface for such a controller using a Web browser program.
Industrial controllers are special purpose computers used for the control of industrial processes and the like. While executing a stored control program, they read inputs from the controlled process and, per the logic of the control program, provide outputs to the controlled process.
Industrial controllers differ from conventional computers in two major respects. First, the architecture of the industrial controller allows it to be easily reconfigured to meet the demands of the particular process being controlled. Normally, the industrial logic controller is in a modular form, and the user selects different modules to be assembled together in a rack and linked together on a backplane in the rack. Varying numbers of inputs and outputs are accommodated with input/output (I/O) modules that may also fit in the rack or in a remote rack connected to the first rack over a control network.
The adaptability of the industrial controller to the controlled process is also enabled by custom written programs executed on the industrial controller, both for the control of the industrial process and to provide human machine interfaces (HMIs), the latter which often depicts a graphic representation of all or part of the process animated to show its current operating state.
Industrial controllers also differ from conventional computers in that they must provide highly reliable and predictable operation. To achieve this end, communications between the industrial controller and I/O are carefully regulated, for example, by being subject to maximum response times, and monitored for errors.
At times, it can be desirable to monitor or control an industrial process from a site that is remote from the industrial controller and the process itself. Such remote operations are well known, for example, using dedicated phone lines and proprietary communication protocols between the industrial controller and a remote HMI. With the development of the Internet and the World Wide Web, dedicated phone lines may be replaced with Internet-based communications between a remote program and a Web server communicating with or incorporated as part of the industrial controller. The promise of the Web is that any Internet connected computer can become a remote terminal for an industrial controller.
Widespread use of Internet based remote operation of industrial controllers is hampered by the need to carry specialized software for the remote computer allowing it to communicate with the industrial controller. Programs implementing, for example, complex graphical remote human-machine interfaces, can be so large as to be cumbersome to transport and load onto the remote machine. Software maintenance of many such remote programs, each of which may be customized to a particular industrial controller, is extremely difficult.